This invention relates to heat-recoverable articles, and more particularly to a heat-recoverable article suitable for use, for example in sealing or insulating a surface of a substrate.
Frequently fluid-carrying conduits laid underground, especially gas pipes, become damaged either by corrosion, cracking or failure of the joint between adjacent sections of pipe, leading to leakage of the fluid from the conduit. A system has been proposed for internal sealing of damaged pipes which utilises an expandable rubber bag or "pig" to press a thin flexible non-resilient metal sheet coated with an ambient-temperature curing adjesive against the internal surface of the pipe. However, this system suffers from the disadvantage that it is difficult to obtain a good seal to an uneven surface.
In recent years increasing attention has been paid to the use of heat-recoverable articles exhibiting the property of elastic memory, for providing environmental insulation to substrates such as fluid-carrying conduits, pipelines and the like. An article having this property is one which has been deformed from an original heat-stable dimensional form into a different heat-unstable form. While this article is maintained below a certain temperature, it will retain its unstable form, but when it is heated to above this temperature, termed the recovery temperature, it will recover towards its original form. However, the term "heat-recoverable" as used herein also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
In British Patent No. 1,062,870 to Raychem Corporation there is disclosed and claimed a heat-recoverable article comprising a resilient member in tubular form, the tube being circumferentially interrupted, for example longitudinally split, to permit changes in the radius thereof and a fusible member which retains the resilient member in a dimensionally unstable form, the arrangement and the material of the members being such that at least a part of the fusible member is positioned in the path of recovery of the resilient member, and that upon raising the temperature of the fusible member to a temperature at which is insufficiently rigid to retain the resilient member in its dimensionally unstable form, the resilient member recovers towards its stable form and thereby urges at least some of the material of the fusible member in the direction of recovery. It is also disclosed that an article comprising a tubular radially expansible resilient member with a surrounding fusible member is particularly suitable for the lining of tubular members such as pipes.